When patients are being mechanically ventilated on an intensive-care ward, for example, the patient to be ventilated is connected pneumatically to the respirator by a system of ventilation tubing. Because the breathing gas supplied to the patient must be adjusted with respect to temperature and humidity to meet the physiological needs of the patient, a respiratory humidifier is arranged in the inhalation or inspiration tube to heat and humidify the breathing gas. The respiratory humidifier usually comprises a liquid container filled with distilled water, the bottom plate of the container being in thermal contact with a heating plate in the housing, as a result of which the liquid is warmed. The inhalation gas is conducted into the liquid container, is thus humidified, and then leaves the liquid container at a certain temperature.
On the one hand, the temperature of the breathing gas is usually measured by the use of a temperature sensor arranged near the patient, the sensor being connected by an electrical measurement line to a control unit, which is arranged in the respiratory humidifier, for example. On the other hand, the temperature of the breathing gas is measured inside the respiratory humidifier, preferably as it enters and as it leaves the liquid container. The measured values are sent to a control unit present in the respiratory humidifier, which regulates the heating output of the humidifier.
Pyrometers or radiation thermometers for contactless temperature measurement are known in the art. These operate on the basis of the fact that every body with a temperature above 0 K emits thermal radiation; the intensity and position of the point of maximum emission depend on the temperature of the body. This radiation is detected and evaluated by the pyrometer. For temperature measurements around room temperature (from about 10° C. to about 40° C.), wavelengths in the mid-infrared region (MIR) will be used.
DE 10 2007 037 955 A1 discloses a contactless temperature-measuring device for a respiratory humidifier with a flow channel; in this device, a closed, hollow body for recording the temperature projects into the flow channel, and an infrared detector is directed toward the inside surface of the hollow body projecting into the flow channel. The disadvantage of this design of a temperature-measuring device is that it is not easy to manufacture a flow channel with a hollow body projecting into it, because either the hollow body must be formed out of the same material as the flow channel or perhaps bonded to it in a second production step, or alternatively the flow channel and the hollow body must be produced by means of separate molds, which is complicated and expensive. In addition, the hollow body in the flow channel is responsible for a relatively high flow resistance, which interferes with the flow of the breathing gas stream and thus reduces the flow rate.
It is therefore the object of the present invention to provide a temperature-measuring device for a respiratory humidifier which can be produced easily and at low cost and which nevertheless makes reliable contactless temperature measurement possible.
This object is achieved by the features of claim 1. Advantageous elaborations and embodiments are described in the subclaims.